Metal bonded abrasive article



May z, 195o n i A. L BAU. mL u j 2,506,556

A METAL BONDED ABRASIVE ARTICLE f Filed Apr'l 2, 1946'- ALBERT l.A BALL lNl/ENoRs.

CARL @Ross By u Patented May 2, 1950 il.. S y

METAL BONDED ABRASIVE ARTHCHJE Application April 2, 1946, Serial N0. 658,976

' 6 Claims. i

This invention relates to grinding wheels and specically to grinding wheels utilizing a metal bond for diamond abrasive.

One obj ect of the present invention is to provide a metal-bonded abrasive wheel in which the backing or supporting portion of the wheel is of ditferent composition from that of the grinding portion. Another object of the invention is to provide a metal-bonded abrasive wheel which will be resistant to warping or distortion during sintering. Another object of the present invention is to make a metal-bonded abrasive wheel which will have a hard, rigid, metallic backing or supporting portion even though sintering is carried out at comparatively low temperatures. Other objects of the invention will be perceived from the following description thereof.

Many diamond abrasive wheels are so constructed that the diamond abrasive is contained only in that portion of the wheel where cutting is desired while the remainder of the wheel is composed only of or very largely of metal. In common practice the same metal is used for bonding the cutting portion and the backing or supporting portion of the wheel, the only difference being that in the cutting portion there is also abrasive. Such vabrasive wheels are customarily produced from mixtures of metal powders, the backing or supporting portion being molded from metal powders alone or with small amounts of filler or lubricant and the cutting portion being molded from a mixture of the metal powders and diamond abrasive, the two portions being then sintered into an integral body. The metal powders most generally used in the making of sintered diamond abrasive articles are copper and tin, the two metals being usually combined in proportions such as those in bronze.

It has been found that such metal bonded abrasive wheels have a tendency to distort or warp during sintering. It is believed that the tendency to distort, particularly in the case of wheels of substantial thickness, is caused by difierential shrinkage occurring in the backing or support. As the temperature is raised during sintering the pressed metal powder of the wheel expands until the sintering temperature is reached. When sintering begins shrinkage occurs, with the top of the wheel being free to shrink somewhat more than the bottom thereof since the bottom of the wheel is, during sintering, in contact with a plate or bat and the friction between the bottom of the wheel and the bat tends to retard shrinkage. Another possible cause of distortion or warping in some cases is the difier- 2 ence between the expansion and contraction oi the backing or support of the wheel and of the abrasive portion thereof. This is a result of the fact that the abrasive portion and the backing or supporting portion are not the same even though the same alloy is used since the abrasive portion has its coeicient of expansion modified by the presence of the abrasive.

It has been found that grinding wheels which are practically free of distortion or warping may be produced if the backing or supporting portion of the wheel is formed from a metal powder or a mixture of metal powders which produce at sintering temperatures a strong metal body without ever becoming sufliciently plastic to permit differential shrinkage. This result may be obtained with abrasive wheels in which the bond for the abrasive is formed primarily from copper and tin powders, for example bonds such as are disclosed in Boyer Patent No. 2,137,329, issued November 22, 1938, by employing iron powder or a mixture of iron, copper and tin powders for the backing or supporting portions. It will be realized that the strength of a sintered powdered metal article will depend to a considerable extent, par ticularly with comparatively low sintering temperatures, upon the density or degree of consolidation imparted by pressing prior to the sintering. The choice, therefore, as to whether to use a support or backing of iron alone or a mixture of iron, copper, and tin will depend pri marily upon the type of iron powder which is employed and the consolidating pressure which is to be used. Thus, certain iron powders derived by electrolytic methods may conveniently be used alone since only moderate consolidating pressure will produce a pressed article the sintered strength of which is satisfactory. On the other hand, een tain iron powders derived by hydrogen reduction methods will normally be used in admixture with copper and tin powders since the high pressure necessary for adequate consolidation of the iron powder is, in general, impractical. Where a sintered support or backing of iron alone is employed. it has also been found that the possibility oi warping or distortion due to differences between the coeicients of expansion of the backing or supporting portion and the abrasive portion will be practically eliminated.

Tests have shown that sintered powdered iron has a thermal expansion coeicient of about 12.5 x 105/ C. while an abrasive ring with a bond formed from `copper and 10% tin powders with about 11% by weight of diamonds has a thermal expansion coeiiicient in the range from 11.9 to 12.9 x 10/ C. This close relationship, it will be seen, explains the reason for the avoidance of dimculty due to differential thermal expension.

In the drawing, Figure 1 represents a plan view of a peripheral grinding abrasive wheel.

Figure 2 represents a section on line 2-2 of Figure l.

Figure 3 is a sectional view of a face grinding abrasive wheel of the so-called cup type.

Figures 4. 5, and 6 illustrate steps in the molding of a diamond abrasive wheel such as that shown in Figures 1 and 2.

The metal powders used in carrying out the present invention may be of the commonly available commercial types and should be comparatively pure to permit regulation of the extent of alloying by adjustment of the sintering temperature and time. Such metal powders are preferably oi' 200 mesh and ner size.

The molding of a peripheral grinding wheel of the type shown in Figures 1 and 2 in which a metal core or backing I surrounds an arbor hole Il and has formed integrally therewith an abrasive rim II is shown in Figures 4, 5, and 6. In Figure 4 a mold block or plunger I5 is provided with a central pin or plug Il and a closely tting mold ring I6. A mixture ofiron, copper, and tin powders in an amount calculated to be suillcient to make a wheel center of the desired thickness is then placed on plunger I5 in the cavity formed by the ring I6 and pin I1 and is spread evenly therein.

Upper mold plunger I5a is then put in place and consolidating pressure which may be as high as 15,000 to 20,000 p. s. i. is applied to the plungers I5 and I5a. After this preliminary consolidation of the backing or support there is placed around mold ring I6, as shown in Figure 5, an outer mold ring. I9 and the mixture of diamond abrasive and metal powder` needed for the abrasive rim is spread evenly in the space between plunger I5a. and mold ring I9. An upperring IGa is then inserted into the assembly in such position that it will operate to compress the abrasive mix against ring I6 and the whole mold assembly is again subjected to pressure. As shown in Figure 6, the abrasive rim and the backing or support are brought together into line as the mold is closed and suitable pressure which may in some cases be as much asr 50,000 to 75,000 p. s. i. or more is then applied. 'Ihe effect of this pressure is to cause unification of the abrasive rim and they metallic backing or supporting portion so that the pressed wheel may be handled as an integral body without danger of separation.

In Figure 3 there is shown a sectional view of a form of abrasive wheel which is intended for grinding on the face or sides.- Here the cutting portion I3 molded from a mixture of abrasive and metal powders is formed integrally with a backing or supporting portion I3a which, in accordance with the present invention, is molded from a mixture of iron, copper and tin powders. The molding may be carried out, so far as the mechanical procedure is concerned, in accordance with known practice. Rings I3 and I 3a, after sintering. are attached to a mounting I4 by any suitable means. Mounting Il may be constructed of any desired material, for example metal or resinoid and may also, of course, be of any desired shape or configuration with such provision for installation on a grinding machine or spindle as is necessary.

Alter removal from the mold, abrasive wheels tain thorough sintering, the hardness of the bond being determined largely by the temperature at which the sintering is carried out. This is weil known in the art and the hardness may be reguy lated as desired.

It has been found that the composition of the backing or support can be varied considerably with the percentage of iron, varying between about 90% and that of copper and tin varying between about 8-18% and 14%, respectively. A sintering temperature of 800 C. may be employed. with good results since at this temperature the backing or supporting portion is well sintered but remains firm and supports the rim against slumpng or distortion.

In the foregoing description abrasive wheels of the type shown in Figures 1 and 2 have been described as having a metal support or core which extends from the abrasive peripheral rim to the arbor hole. It will be realized that with large Wheels the amount of metal in such a construction will be large and accordingly the weight of the wheel will be excessive. With large wheels, therefore, it will frequently be desired to have the metal core or support extend inwardly from the abrasive rim only a relatively small distance, of the order of 1 to 18 times the thickness of the abrasive rim depending on the size of the wheel, and to have the rest of the core or support formed from some lighter material such as a moldable plastic which can be attached in any suitable manner to the metal support or which may be molded in situ inside the metal supporting ring. Wheel constructions of this type are intended to be within the scope of the present invention since the advantages of the present invention are inherent therein even though the entire support is not formed of metal.

The proportion of diamond employed in the abrasive rim of the wheel is not critical and will vary with the purpose for which the wheel is intended. Other types of abrasives might be used instead of diamonds although it has been found that except in very rare cases the expense of metal bonds is not warranted except for an expensive abrasive such as diamond. However, so far as the present invention is concerned, it will be operative with and it is intended to cover abrasive wheels made with all types of abrasive materials such as alumina, silicon carbide, boron carbide, emery, titanium carbide, and the like.

Furthermore although the invention has been described with particular reference to bonds obtained by sintering mixtures of copper and tin powders, it is applicable also to bonds of that type containing other alloying elements such as iron, nickel, zinc, aluminum, etc.

Where the term support is used in the claims it is intended to include and be broad enough to cover backngs and other integral sintered supporting members. Where percentages are specied in the claims they are percentages by weight.

It will be understood that there are many other obvious changes and variations that may be made in the method of carrying out the invention which has been described above and it will be understood that all such variations and changea are meant to be comprehended within the present invention and that the invention may be utilized in producing abrasive articles other than wheels.

It is not intended that the invention shall be limited except by the scope of the following claims:

We claim:

1. A metal-bonded abrasive article comprising s sintered abrasive portion containing a minor proportion of abrasive particles and a bond comprising the sintered reaction product of a major proportion of copper powder and tin powder in an amount up to about 20% of the weight of said bond, and an integral, sintered, non-abrasive metal support for said abrasive portion selected from the group consisting of (l) sintered iron powder and (2) 8090% iron powder, 8-18% copper powder and 1-4% tin powder in sintered form.

2. A metal-bonded abrasive article comprising a sintered abrasive portion containing about 11% of diamond abrasive particles and a bond comprising the sintered reaction product of a major proportion of copper powder and tin powder in an amount up to about 20% of the weight of said bond, and an integral, sintered, non-abrasive metal support for said abrasive portion comprising the sintered reaction product of about iiD-90% iron powder, 848% copper powder, and 14% tin powder.

3. A metal-bonded abrasive article comprising a sintered abrasive portion containing a minor proportion of diamond .abrasive particles and a bond comprising the sintered reaction product of a major proportion of copper powder and tin powder in an amount up to about 20% of the weight of said bond, and an integral, sintered, non-abrasive metal support for said abrasive portion comprising the sintered reaction product of about Sii-90% iron powder, 848% copper powder. and 14% tin powder.

4. A metal-bonded abrasive article comprising a sintered abrasive portion containing a minor proportion of diamond abrasive particles and a bond comprising the sintered reaction product of a major proportion of copper powder and tin powder in an amount up to about 20% of the weight of said bond. and an integral, sintered, non-abrasive metal support for said abrasive portion consisting of sintered iron powder.

5. A metal-bonded abrasive article comprising a sintered abrasive portion containing a minor proportion of abrasive particles and a bond com prising the sintered reaction product o a major proportion of copper powder and tin powder in an amount up to about 20% of the weight oi said bond, and an integral. sintered, non-abrasive metal support for said abrasive portion comprising the sintered reaction product of about -90% iron powder. 8.18% copper powder and 1-496 tin powder.

6. A metal-bonded abrasive article comprising a sintered abrasive portion containing a minor proportion of diamond abrasive particles a bond comprising the sintered reaction product of a major. proportion of copper powder and tin powder in an amount up to about 20% ot the weight of said bond, and an integral, sintered, non-abrasive metal support for said abrasive portion comprising about 80-90% iron powder, 84.8% copper powder and 14% tin powder in sintered form.

ALBERT L. BALL. CARL G. ROSE.

The following references are of record in the le of this patent:

UNITED STATES PA v, 

